A known occupant detection device detecting an occupant occupying a vehicle seat and transmitting the classification of the occupant to the occupant detection device is described in US2004/0068357A1. With the construction according to the occupant detection device described in US2004/0068357A1 load sensor is reduced in size, and manufacturing cost is reduced by appropriately aggregates each function of the vehicle occupant detection device.
More particularly, the occupant detection device described in US2004/0068357A1 includes a load sensor for outputting load data applied on a vehicle seat, and a control device having a calculation portion for classifying an occupant on the basis of an output from the load sensor. The load sensor is configured to output the load data as analogue voltage, and the control device includes an analogue-digital converting portion for converting analogue voltage to digital data. The control device transmits judgment result encoded at the calculation portion to the vehicle occupant protection device. Thus, the load sensor which does not include the analogue-digital conversion function can be reduced in size and simpler. Further, because the judgment result is encoded, signal error of the data transmitted to the vehicle occupant protection device can be easily detected, and thus reliability of the transmitted data can be improved.
Notwithstanding, generally, plural load sensors, particularly, 3-4 load sensors are provided on each vehicle seat. Thus, the control device requires analogue-digital converters (i.e., A/D converter) corresponding to the number of load sensors. Although the multiple load sensors may be provided on a single vehicle seat using a single A/D converter via an analogue multiplexer, or the like, necessity of the analogue multiplexer and circuits, or the like, for controlling thereof increases the circuit of the control device in size. There are large number of sources of noise such as audio equipment, an indoor unit of ETC (i.e., an electronic toll collection system), and a navigation system, for vehicles recently. Thus, when transmitting the load data as analogue signal to the control device, the possibility that the noise is overlapped on the analogue signal is highly increased, which is not favorable for detecting an occupant sitting on the vehicle seat.
Further, the vehicle occupant protection device for transmitting digitalized and encoded signal can be constructed to detect that the signal was not enable to be transmitted properly because of signal error, or the like. However, with the vehicle occupant protection device, for example, an airbag device, or, a seatbelt device, it is not favorable that the detection data of the occupant cannot be obtained when the vehicle occupant protection device has to conduct important control such as at vehicle collision even if improper transmission of the signal can be detected.
A need thus exists for an occupant classification device for a vehicle which accurately transmits load data by improving noise-proof.